Research On The Secretion And Release Of Free Cyanobacterial Extracellular Polymeric Substance And Its Migration During Water Treatment

Cyanobacterial extracellular polymeric substance(EPS)is characterized by high contents of organic matter,and the free cyanobacteria EPS has become one of the main pollution sources in source water due to the huge emission and the difficulty removal.This paper mainly focuses on the organic pollution of free cyanobacteria EPS in the algal blooms,from the angle of drinking water safety,analyzes the regularity of its natural secretion in different environmental conditions.The removal efficiency of free cyanobacteria EPS on the basis of different pre-oxidation treatments has been contrasted.To assess the potential of residual free cyanobacteria EPS in treated drinking water,we explore the removal efficiency of free cyanobacteria EPS after the conventional physicochemical treatment.In order to select an optimum method of drinking water treatment which based on the removal of free cyanobacteria EPS,the research contents of this paper are as fol ows:(1)We investigated the release situation of free cyanobacteria EPS in source water with different pH,temperature,light and hydrodynamic conditions.In the neutral pH range,the secretion of free cyanobacteria EPS would increase gradually with increasing pH,and the optimum pH value for the formation and secretion of cyanobacteria EPS was 7-8.The acidic conditions were more favorable for the secretion of polysaccharide components than alkaline conditions,however,more likely to cause algae cell damage.Free cyanobacteria EPS tend to be formed and secreted under the condition of light.However,the difference in light intensity has little effect on the secretion of cyanobacterial EPS.In the case of certain illumination,25 ? is the best condition that conducive to the formation and secretion of cyanobacteria EPS.Although,both high temperature and low temperature could cause the inhibition of the formation and secretion of free cyanobacteria EPS.The low temperature 10 ? condition is more inhibition than the high temperature 40 0C conditions.The hydrodynamic conditions have little effect on the formation and secretion of free cyanobacteria EPS.In general,relative to low-speed agitation,high-speed agitation could stimulate the secretion and release of cyanobacteria EPS.(2)We using KMnO4 and NaClO as pre-oxidants to explore the degradation and the removal effects of free cyanobacteria EPS by different pre-oxidation conditions.The results showed that both KMnO4 and NaCIO had obvious degradation regulation on free cyanobacteria EPS,and the degradation regulation effect increased with the increasing pre-oxidant amount.However,the oxidation effects of the two pre-oxidants are significantly different.In the same dosage conditions,the oxidation intensity of NaCIO is better than that of KMnO4,and the damage strength to algae cells is also larger.The preferential degradation rules of KMnO4 and NaClO for composition of the free cyanobacteria EPS are not consistent,but they show a consistent pattern for the molecular weight distribution of free cyanobacteria EPS.Both of them tend to degrade macromolecular chains to small molecules.In summary,it is a safer and more effective pretreatment method that to pre-oxidize the algae-containing waters coexisting with cyanobacteria EPS and algae cells using KMnO4.(3)We explored the effects of interception and removal of free cyanobacteria EPS of drinking water in the routine physicochemical treatment such as coagulation,sedimentation,filtration and disinfection.The removal efficiency of free cyanobacteria EPS increased with the increasing coagulant dosage.However,the optimal removal rate of cyanobacteria EPS was limited when the raw water was directly coagulated and precipitated.The removal efficiency of cyanobacterial EPS was significantly increased by coagulation.The removal efficiency of EPS in algae-containing water before and after filtration was slightly higher than that in non-algae water.It was due to the adhesion of some cyanobacteria EPS in algae-containing water to the surface of residual algae cells.The disinfection process has obvious removal effect on the free cyanobacteria EPS,and the principle is the same as the preoxidation degradation mechanism.Overall,the pre-oxidation+coagulation sedimentation+filtration+disinfection process system is better than the direct coagulation sedimentation+filtration+disinfection process system to remove the free cyanobacteria EPS.For the treatment of algae-containing EPS,2.Omg/L KMnO4 pre-oxidation+40mg/L PAC coagulation sedimentation+filtration+1.5mg/L NaClO disinfection process is the best.